[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

*To*: tesla-at-pupman-dot-com*Subject*: Re: Pole Pig Simulation*From*: "Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)*Date*: Thu, 07 Sep 2000 08:05:39 -0600*Delivered-To*: fixup-tesla-at-pupman-dot-com-at-fixme

Inductors in the circuit subtract VARS, Capacitors add them. If they are all series or parallel, it's fairly easy, but when you have a combination of both, then, as you've noticed, it gets a tad hairy. One approach is to convert the series combination of ballast and pig into a parallel equivalent. Then, you'll have the PFC C in parallel with the inductor in parallel with the "resistance" of the pig (actually the TC load). The classic way to do this right is to use complex impedances. Zl = Rloss+j*omega*L, Zc =ESRc -j/(omega*C), Xpig = Rpig+jXpig. Then, you can use standard series and parallel formulae to figure out the terminal impedance seen by the power line. HOWEVER, I suspect that in a TC application, a simple single frequency impedance calculation won't get a good PF correction. Why? because the current is drawn in little bursts when the spark gap fires and the primary tank charges. The classic PFC equations all assume sinusoidal voltage and current. What you really need to do is calculate V*I at each instant through the cycle, then average them. This gives you true power. Then, take Vrms*Irms, which gives you apparent power. The "reactive power" or "VAR" flow (which doesn't really apply with non-sinusoidal waveforms) is calculated by Apparent Power = sqrt(True Power^2 + Reactive Power^2) The non-sinusoidal nature of the current drawn by a TC is going to be a big problem with power factor, in much the same way as lightly loaded capacitor input rectifiers (which only draw power at the peak of the half cycle). PC switching power supplies caused a lot of problems with this until better power factors were mandated. The problem was particularly severe in offices fed by 3 phase Wye, because the neutral currents were quite high (if you aren't drawing sinusoidal current from the phases, then the neutral currents don't cancel). This actually resulted in changes to the NEC a few years back, requiring heavier neutral conductors. I would venture to say that the PFC might compensate for the ballast, but isn't going going to compensate for the odd power factor from the sparkgap and primary tank cap. For that, you'll need to go to a more sophisticated circuit. ---------- > From: Tesla list <tesla-at-pupman-dot-com> > To: tesla-at-pupman-dot-com > Subject: Pole Pig Simulation > Date: Wednesday, September 06, 2000 6:29 PM > > Original poster: "Barton B. Anderson" <tesla123-at-pacbell-dot-net> > > Hi John C., Terry, > > I'm having a real difficult time with pole pig simulations for power > factor. The problem is the ballast. With a pole pig, it will easily draw > massive amps without any current limiting. I've been reading both your > responses and continue to integrate these more refined details to the > similations. > > With your methods, it necessary to identify the VAR's to calc PF. However, > adding either series R, series L, or PFC, the phase angle between line V > and I change. > > Is it right to say that the PF could also be calculated this way: > > (assume 1 cycle here) > Identify and the time of zero-crossing of line voltage; > Identify the time for zero-crossing of line current; > > Then, ARCCOS(Lead time / Lag time) = degree of phase angle? > This angle can obvisouly be leading or lagging depending on the circuit. > > Again, a ballast really makes a mess of this. As L-Ballast is increased, > the phase angle increases and it also limits current (therefore, any > current or voltage reading past the ballast cannot be used for identifying > a PF based on Volt-Amps or Watts). If the method decribed above will > perform the same function, then I've got some interesting info about > ballast PF correction, but if not I could sure use some ideas. > > > HELP!!!!, > Bart > > >

- Prev by Date:
**Run Time** - Next by Date:
**RE: FIRST LIGHT** - Prev by thread:
**Pole Pig Simulation** - Next by thread:
**Re: Pole Pig Simulation** - Index(es):